relative volume works again

bin/volume

@@ -134,7 +134,9 @@ m*) [ -z "$2" ] || usage
 	exit 0 ;;
 
 r*)
-	! newval=$(printf "%s %s + p\n" $("$argv0"s) "$2" | dc) \
+	set -x
+	argv2="$(printf "%s\n" "$2" | tr - _)"
+	! newval=$(printf "%s %s + p\n" $("$argv0" s) "$argv2" | dc) \
 		&& printf "%b: Error finding new value for volume.\n" "$argv0" \
 		&& exit 1
 	"$argv0" a "$newval"